Interconnected SnO2 nanoflakes decorated WO3 composites as wearable and ultrafast sensors for real-time wireless sleep quality tracking and breath disorder detection

Monitoring human breath is critical for determining human well-being. Most reported humidity sensors are unsuitable for breath monitoring because of their long response and recovery time, poor stability, and high operating temperature. To address these challenges, robust tungsten oxide (WO3) and tin oxide (SnO2) composite sensors were fabricated, and their humidity-sensing properties were investigated. The SnO2/WO3 composites were optimized by altering the SnO2 fraction to achieve high humidity sensitivity. The SnO2/WO3 composite exhibited superior sensing performance (88) than pristine WO3 and SnO2 under 97 % relative humidity. The sensor demonstrated good linearity while altering humidity from 15 % to 97 %, with an R2 = 0.9729. The sensor's rapid response (0.6 s) and recovery (0.6 s) time allow for breath rate monitoring and breath disorder detection. The wearable sensor demonstrated multifunctional human breath detections such as varied breath rates (5–60 breaths per minute), nose blocking for separate nostrils, wireless sleep quality tracking for more than 7 h continuously, and sleep apnea-hypopnea detection via a smartphone. The capabilities of the humidity sensor allow for robust application in sleep quality, sleep apnea, and hypopnea detection.